This is a study of the epidemiology of interstitial cystitis among female participants of two large ongoing cohort studies: the Nurses' Health Study I (121,000 participants) and Nurses' Health Study II (116,000 participants). Interstitial Cystitis is a chronic, painful and disabling disease occurring predominantly in women but remarkably little is known about even such basic epidemiologic factors such as how common this disease is in the US and if it is increasing in frequency. The primary objective will be to determine the prevalence, incidence rates, and age distribution of interstitial cystitis in women. The secondary objective will be to examine the quality of life of women with interstitial cystitis, to compare this to the quality of life of healthy women and also to those with other chronic, painful conditions, and explore how the quality of life changes over a four year period. We will also examine the relation between interstitial cystitis and previously proposed risk factors including autoimmune diseases and multiple urinary tract infections. Finally, we will perform hypotheses generating analyses on proposed risk factors such as estrogen use, dietary factors, and alcohol consumption. Information on the presence of physician diagnosed interstitial cystitis will be collected by biennial mailed questionnaire. All self-reported cases will be confirmed by a supplementary form and a review of medical records. The diagnostic criteria will be that previously recommended by the NlDDK for research studies of interstitial cystitis. Information on exposure variables will also be collected by the biennial questionnaire. Baseline quality of life data, using the Medical Outcomes Study Short-Form 36, were collected within two years of the start of this study and will be updated four years later. Additional exposure information will be obtained by mailed questionnaire from all the cases and a random sample of 500 controls. During the five years of follow-up, over 110 cases of interstitial cystitis will be confirmed. The large sample size and long follow-up period will permit stable estimates of prevalence and incidence rates. In addition, this will provide a power of 0.86 to detect a relative risk of 1.8 for a dichotomous exposure. The morbidity of this chronic disease, the lack of essential epidemiologic information and the extremely limited knowledge regarding risk factors makes this an important public health issue. The proposed study will provide valuable data on the frequency of interstitial cystitis, the impact on the quality of life of women with this disease, and will generate hypotheses regarding risk factors for the development of this disease.